The high morbidity and mortality associated with massive burns are mainly due to bacterial invasion of open wounds. Early closure of burn wounds can prevent this complication. In massive burns, however, donor sites for autologous skin grafts are severely limited, and temporary coverings must be employed until healed donor sites become available. We have recently demonstrated that cultured keratinocyte sheets generated from a small biopsy of unburned skin can be used successfully as autografts in the treatment of massive acute burns. Grafts provide permanent wound closure within a three week period, the length of time required to generate the cultured epithelial sheets. Once placed on the wound bed, cultured grafts attach and differentiate into a normally stratified epidermis within one to two weeks. Preliminary results from long-term follow-up biopsies indicate that the skin regenerated from cultured grafts compares favorably with meshed split-thickness skin grafts of comparable age. The proposed project is a morphologic, morphometric, and immunohistochemical study of cultured grafts in vivo. The study has two major goals: 1) to provide a better understanding of the long-term behavior of the grafts in order to objectively evaluate their clinical usefulness, and 2) to take advantage of this new human biologic system to investigate problems of basic scientific interest in the fields of epidermal physiology and wound healing. The specific aims of the study are to examine changes associated with healing and regeneration of skin from cultured grafts in comparison with conventional split-thickness autografts. Donor site-specific differences in graft healing and differentiation will be examined, and the phenomena associated with epidermal-connective tissue attachment will be studied by the use of monoclonal antibodies directed against basement membrane components and by electron microscopy. Epithelial differentiation will be analyzed using antibodies against different classes of cytoplasmic keratins. Part of the study will examine colonization of grafts by epidermal dendritic cells.